1. Field of the Invention
The present invention generally relates to a status holding circuit and a logic circuit using the same. More particularly, the present invention is directed to a status holding circuit utilizing a hysteresis characteristic and a logic circuit using the same. Further, the present invention relates to a sequential logic circuit called a latch circuit.
2. Description of Related Art
Generally, digital logic circuits are each classified as either a combinational logic circuit or a sequential logic circuit. The output status of a combinational logic circuit is based on only the present input status. On the other hand, the output status of a sequential logic circuit is not based on only the present input status but the present status of the sequential logic circuit as well as the previous input status. Such a sequential logic circuit includes a latch circuit or a flip-flop circuit without exception. A flip-flop circuit can be formed by two latch circuits. From this viewpoint, all types of logic circuits can be configured by only latch circuits and NOR (or NAND) gates. Recently high integration density high-speed LSIs have been demanded. Particularly, there is a trend of an attempt to simplify latch circuits to meet the above-mentioned demand.
Conventionally, normal transistors are used as logic elements for configuring a latch circuit. For example, a D-type latch circuit which is a logic circuit has a D-input and a clock input. An information (data) signal applied to the D-input of the latch circuit is stored therein and then drawn therefrom in synchronism with a clock pulse signal applied to the clock input. A D-type latch circuit based on the transistor-transistor logic (TTL) is formed by a large number of bipolar transistors. A D-type latch circuit based on the emitter-coupled logic (ECL) is formed by at least seven transistors. That is, there is a need for a large number of transistors which configure a latch circuit. Additionally, the use of a large number of transistors prevents high integration and high speeds.